Penny doubled for 30 days: the $1 million choice
Would you take $1 million now, or a penny that doubles every day for 30 days? Pick first, then watch every day play out. Free, no sign-up.
The penny is a puzzle. Their allowance is real.
In the Penny Time app, your child can back small made-up ventures with part of their own allowance on their own phone or tablet, then wait a few days to see how it turned out.
Would you take $1 million now, or a penny that doubles every day for 30 days?
What if? Change the deal (this starts a new round)
Day 1 of 30
$0.01
Liked watching money grow? Try a real decision.
Penny Time quests let your child back a small made-up venture with part of their own allowance, on their own phone or tablet, and wait a few days for the result. What they put in always comes back and only the reward is at stake, so they learn about patience and risk without losing a cent.
How much is a penny doubled for 30 days?
A penny doubled every day for 30 days is worth $5,368,709.12 on day 30. That count treats the first penny as day 1, so the penny doubles 29 times. It does beat $1 million, but only near the end: the penny is worth $671,088.64 on day 27 and passes $1 million on day 28, when it reaches $1,342,177.28.
For the first three weeks it looks like a bad deal. On day 20 the penny is worth $5,242.88. Every day adds as much money as the pile already holds, so the last few days bring in almost all of the $5.4 million. That is compound growth: new money earns money too. In Penny Time's penny game, your child picks the penny or the million first, then watches the month unfold one day at a time.
How the game counts the days
Day 1 is the first penny. It doubles overnight, so day 2 is 2 cents, day 3 is 4 cents and day 10 is $5.12. By day 30 the penny has doubled 29 times. Our compound interest calculator's penny table counts the same way.
Sites that start at day 0 get one more doubling, which gives $10,737,418.24 on day 30. Sites that add up every day's amount, as if you were paid the penny each day, get $10,737,418.23. Both answer a slightly different question, so check which one your child is working out.
When spending is turned on, the game works in whole cents and rounds each day's spending down, because you can't spend half a cent.
A penny and a dollar doubled for 30 days, day by day
Here is every day up to day 31 for both starting amounts. The first day each column passes $1 million is in bold: day 28 for the penny and day 21 for the dollar.
| Day | Start with 1 cent | Start with $1 |
|---|---|---|
| Day 1 | $0.01 | $1.00 |
| Day 2 | $0.02 | $2.00 |
| Day 3 | $0.04 | $4.00 |
| Day 4 | $0.08 | $8.00 |
| Day 5 | $0.16 | $16.00 |
| Day 6 | $0.32 | $32.00 |
| Day 7 | $0.64 | $64.00 |
| Day 8 | $1.28 | $128.00 |
| Day 9 | $2.56 | $256.00 |
| Day 10 | $5.12 | $512.00 |
| Day 11 | $10.24 | $1,024.00 |
| Day 12 | $20.48 | $2,048.00 |
| Day 13 | $40.96 | $4,096.00 |
| Day 14 | $81.92 | $8,192.00 |
| Day 15 | $163.84 | $16,384.00 |
| Day 16 | $327.68 | $32,768.00 |
| Day 17 | $655.36 | $65,536.00 |
| Day 18 | $1,310.72 | $131,072.00 |
| Day 19 | $2,621.44 | $262,144.00 |
| Day 20 | $5,242.88 | $524,288.00 |
| Day 21 | $10,485.76 | $1,048,576.00 |
| Day 22 | $20,971.52 | $2,097,152.00 |
| Day 23 | $41,943.04 | $4,194,304.00 |
| Day 24 | $83,886.08 | $8,388,608.00 |
| Day 25 | $167,772.16 | $16,777,216.00 |
| Day 26 | $335,544.32 | $33,554,432.00 |
| Day 27 | $671,088.64 | $67,108,864.00 |
| Day 28 | $1,342,177.28 | $134,217,728.00 |
| Day 29 | $2,684,354.56 | $268,435,456.00 |
| Day 30 | $5,368,709.12 | $536,870,912.00 |
| Day 31 | $10,737,418.24 | $1,073,741,824.00 |
Look at day 20: the penny is at $5,242.88 while the dollar is past half a million. Starting with 100 times more money gets you to $1 million a week sooner, and one more week of doubling gets the penny there too.
Why doubling is compounding
Compounding means the money you earn starts earning money too. The penny grows by 100% a day, and each day's growth joins the pile before the next day starts, so every doubling is bigger than the one before. On day 29 the penny gains $1,342,177.28 in a single day. On day 30 it gains $2,684,354.56.
Real money compounds the same way, only far more slowly. The Rule of 72 shows how slowly: divide 72 by the yearly growth rate to get roughly how many years it takes to double. At 6% a year that is about 12 years. The penny does it in one day, which is why it works as a puzzle but not as a plan.
What real savings look like
No bank account doubles money overnight. The FDIC national average rate on savings accounts was 0.37% a year in September 2026. At that rate the Rule of 72 gives about 195 years to double. Some accounts pay more than the average, so here is $100 at 5% a year next to $100 at 0.37%.
| After | At 5% a year | At 0.37% a year |
|---|---|---|
| 1 year | $105.00 | $100.37 |
| 5 years | $127.63 | $101.86 |
| 10 years | $162.89 | $103.76 |
| 15 years | $207.89 | $105.70 |
| 20 years | $265.33 | $107.67 |
| 30 years | $432.19 | $111.72 |
Interest added once a year. Real rates move up and down; the table holds each rate steady to show the gap. Source: FDIC National Rates and Rate Caps, September 2026 (rates checked September 2026).
At 5% a year, $100 takes about 14 years to become $200. The penny in the game doubles 29 times in 30 days. Show your child both numbers side by side. Growth on top of growth is real, it just takes years, so the earlier money starts, the more doublings it gets.
Talking points by age
Ages 6-8: play together and read the numbers out loud. Before you start, put real pennies on the table and double them for a few days: 1, 2, 4, 8, 16, 32. Day 7 needs 64 pennies, and most families run out soon after. Keep the talk to one idea: doubling means getting a copy of everything you already have.
Ages 9-12: ask your child to guess the day the penny passes $1 million before you press play (it is day 28). Then turn on spending half of each day's new money and ask why the ending shrinks from over $5 million to about $2,000. Spend the growth and there is less left to grow.
Ages 13 and up: show the formula. The value on day n is 1 cent times 2 to the power of n minus 1. Compare it with 5% a year and work out how long real money takes to double. Then ask: if someone online promised to double your money in a month, what would you think? The investing for teens guide is a good next step.
Using the penny game in class
The game runs in the browser with no accounts, and the big numbers read well on a projector. A 15-minute plan:
- Read the question out loud and take a vote: the million or the penny.
- Pick the class's answer, then press Next day for the first 10 days. Ask everyone to guess the day the penny passes $1 million.
- Press Play for the rest of the month and check the guesses.
- Change the deal to 25 days, then to spending half the new money, and vote again.
Questions for the debrief:
- Why did the penny look like a bad deal for so long?
- What changed when you spent part of the new money?
- Where in real life does money grow on top of itself?
More free lessons and games for teachers are on our classroom page.
From a puzzle to real money
A penny that doubles every day doesn't exist, but the choice underneath it does: spend now, or let money work and wait. Penny Time gives kids that choice with their own allowance. Its quests pitch small made-up ventures, and your child decides whether to back one with part of their balance and wait a few days for the result. What they put in always comes back, and only the reward is at stake. No phone or tablet for them yet? You can still track their allowance in the app from your own phone.
Educational only. The doubling penny is a thought experiment, not a real way to grow money, and the 5% rate is an example, not a promise of what any account pays. This is not financial advice.
Frequently Asked Questions
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Yes. Counting the first penny as day 1, it is worth $5,368,709.12 on day 30, after 29 doublings. It stays under $1 million until day 28, when it reaches $1,342,177.28.
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If you are paid a penny on day 1, 2 cents on day 2 and so on, your pay on day 30 alone is $5,368,709.12 and your total pay for the month is $10,737,418.23. Some sites quote $10,737,418.24 instead, which is what you get when the first penny counts as day 0.
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Take the penny, as long as you can wait all 30 days: it ends at $5,368,709.12. If the deal were 27 days or fewer, the million would win, because the penny is only worth $671,088.64 on day 27.
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A dollar that doubles every day is worth $536,870,912 on day 30, counting the first dollar as day 1. It passes $1 million on day 21, when it reaches $1,048,576.
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No. The FDIC national average rate on savings accounts was 0.37% a year in September 2026. Even at 5% a year, the Rule of 72 says money takes about 14 years to double, not one day.
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Kids 6 to 8 can play with a parent reading the numbers out loud. Kids 9 to 12 can play on their own and guess the day the penny passes $1 million. Teens can check the math with powers of 2 and compare it with real interest rates.
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Yes. It is free, runs in any browser with no sign-up, and the big numbers and bar chart are easy to read on a projector.
Raise kids who understand how money works
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